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pgsql: Fix race condition in preparing a transaction for two-phase comm 6+ messages / 1 participants [nested] [flat]
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/bb38fb0d43c8d7ff54072bfd8bd63154e536b384 Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ REL9_3_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/48fc8962f9f1ec456735500795ba894c5da9e89a Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ REL9_2_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/d8dbeb048287f478f11eeab005ddd1e9df65a4d9 Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ REL9_1_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/8c19b807c49aaaa18d1a166df5649ec2c04df320 Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ REL9_0_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/82a83ec6841dc598af5a47a45989fd969e3099a5 Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
* pgsql: Fix race condition in preparing a transaction for two-phase comm @ 2014-05-15 14:18 Heikki Linnakangas <heikki.linnakangas@iki.fi> 0 siblings, 0 replies; 6+ messages in thread From: Heikki Linnakangas @ 2014-05-15 14:18 UTC (permalink / raw) To: pgsql-committers Fix race condition in preparing a transaction for two-phase commit. To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. Branch ------ REL8_4_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/045fbbdc4495aa38dcf36b37ae6db5b50d5e5c3a Modified Files -------------- src/backend/access/transam/twophase.c | 169 ++++++++++++++++++++++++--------- src/backend/access/transam/xact.c | 19 +++- src/include/access/twophase.h | 3 + 3 files changed, 144 insertions(+), 47 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers ^ permalink raw reply [nested|flat] 6+ messages in thread
end of thread, other threads:[~2014-05-15 14:18 UTC | newest] Thread overview: 6+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi> 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi> 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi> 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi> 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi> 2014-05-15 14:18 pgsql: Fix race condition in preparing a transaction for two-phase comm Heikki Linnakangas <heikki.linnakangas@iki.fi>
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